Resistance for electric heating devices



RESISTANCE FOR ELECTRIC HEATING- DEVICES Filed March 9, 1951 Patented Feb. 19, 1935 PATENT OFFICE RESISTANCE FOR ELECTRIC HEATING DEVICES Etienne Challet, Paris, France Application March 9, 1931, Serial No. 521,364 In Belgium March 10, 1930 1 Claim.

The present invention relates to the use of an electric heating wire for the manufacture of a conductor having a flat cross-section, thus affording an optimum efiiciency due to its large surface of contact; said flat conductor is provided with suitably spaced pointed studs adapted for insertion into the backing substance, which usually consists of asbestos, and upon which the conductor is placed or wound, thus giving it a fixed position whereby all short-circuits will be obviated.

This arrangement obviates all defects due to constructions in which it is desired to obtain a high efliciency by placing the wire upon the nonconducting and refractory surface of the heating device of which it forms a part.

In fact, when a round wire is employed, it becomes very difficult to hold the spiral turns,

' and chiefly when the direction is to be changed. On the other hand, the device affords a low efliciency, since the wire does not touch the part which it is to heat, it being usually separated therefrom by mica, and thus has only a line or generatrix in contact, the remainder of the wire acting only by radiation.

If band or strips are employed, this occasions two serious drawbacks in the construction, in spite of the high efliciency thus obtained. In the first place, it is practically impossible to attach the spiral turns or to secure the band when the direction is changed, due to its reduced thickness, and chiefly in domestic apparatus, and secondly, it is practically impossible to wind the band flatwise when a flat heater is to be constructed.

In this case, the band is simply wound around a piece of mica, and it is held between insulating members. In these conditions, the part of the band next the part to be heated will give the maximum efficiency, whilst in the other part, situated on the other side of the insulating support, the heat which it produces must first traverse the insulation about which the band is wound, and then a layer of air having the same thickness as the band, and finally the mica of the insulation, and thus it will obviously show a very small efliciency.

The present invention obviates all such defects. For this purpose, the resistance wire, of round, square or other cross-section, is disposed according to the desired outline upon a matrix having recesses at suitable intervals which are perpendicular to the direction of the wire. The wire thus disposed is flattened by a pressing tool or hammer, and the wire is thus given the shape of a band, save at the parts corresponding to the said recesses, into which it enters in order to form the attaching studs.

The resistance element thus prepared is then mounted on a sheet of asbestos, and on it is dis- 5 posed a sheet of mica, and also the metallic part which is to be heated.

In the case of circular heating bodies, it is simply necessary to treat a round wire between in a rolling mill, in which one roller is recessed ac- 10 cording to generatrices and the other is smooth. The wire is thus ready to be wound, with its fiat surface in contact with the mica and adjacent the part at which the heat is to be used.

The accompanying drawing shows by way of y example various embodiments of the invention.

Fig. 1 is a cross-section of a wire in its flattened part, with the stud E extending downwardly.

Fig. 2 is an elevational view of the wire, showing the situation of the studs E, the flattened part F, and the face G in contact with the asbestos.

Fig. 3 is a cross-section of the same wire through the stud which shows at E that the round section of the wire is maintained. 25

Fig. 4 is a plan view of the flattened resistance element.

Figs. 5 and 6 show the wire before and after the flattening by which the studs are formed. The untreated wire H enters the recesses I in order to form the stud E. The matrix is disposed at J and K is the lower face of the pressing tool. Fig. 6 shows the stud formed at E.

Figs. '7, 8 and 9 show the wire mounted in the main body of the heater. The stud is inserted into the asbestos O which is mounted on the main support of the heating body P. Themica insulation is disposed at M, and at L is the part to be heated.

Figs. 10, 11 and 12 are sectional and elevational views of a wire which has been treated in a rolling mill, and. which differs slightly from the wire resulting from the pressing process, since it has a uniform thickness, as the rolling process lengthens the wire without widening it, on the contrary to what occurs in the pressing process.

Having described my invention what I claim as new and desire to secure by Letters Patent is:

A heating element comprising a support, an insulating block, a flattened wire provided with studs adapted for insertion into said insulating block, an insulating plate disposed upon the flattened face of the wire, and a heating plate mounted upon said insulating plate.

ETIENNE CHALLET. 66 

